Temperature dependence of protein-induced flocculation of phosphatidylcholine liposomes

We studied the influence of the ambient temperature on the lysozyme- and cytochrome c-induced flocculation of phosphatidylcholine liposomes and its relation to the adsorption of the proteins at phospholipid membrane surfaces. The temperature dependence of two kinetic parameters, flocculation rate and activation energy, was experimentally determined. From 10 to 45 degrees C, the maximum increase in the activation energy was on the order (4-5) x 10(-20) J/particle (about 8-10 kT). The influence of the temperature was more emphasized on the values for the flocculation rate, which was the primary calculated parameter, rather than for the activation energy. Within the studied temperature range a Ei-fold increase in the relative flocculation rate was observed in the case of 1.0 mg/mL cytochrome c-induced liposome flocculation. The temperature dependencies of the activation energy and the flocculation rate were considered in terms of Brownian motion of the phosphatidylcholine liposomes, protein adsorption mechanism, and bridging mechanism of the protein-induced liposome flocculation.